$namespace: 'yy' !default;
$block-sel: "-" !default;
$elem-sel: "__" !default;
$mod-sel: "--" !default;

@mixin b($block) {
  $B: #{$namespace + $block-sel + $block};
  .#{$B} {
    @content;
  }
}

@mixin e($el) {
  $selector: &;
  //跳出嵌套
  @at-root {
    #{$selector + $elem-sel + $el} {
      @content;
    }
  }
}

@mixin m($m) {
  $selector: &;
  //跳出嵌套
  @at-root {
    #{$selector + $mod-sel + $m} {
      @content;
    }
  }
}

@mixin bfc{
  height: 100%;
  overflow: hidden;
}